I've ran some benchmarks on a few 1920x1080 clips. When temporal radius was turned on and maximum allowed gpu memory usage was set lower than 100%, most of the time it will increase the speed.

My machine is a i7 4770k @ 4.3Ghz, GeForce GTX 650 Ti Boost @ 1Ghz. When I ran benchmark with use cpu+gpu, memory allowed usage to 100%, I would get around 9.6fps. But when I lower it to 35%-50%, I would get 11fps.